1. Field of the Invention
The invention is based on a device for restoring a rotary member into a defined normal position, in particular for restoring a throttle valve shaft, which supports a throttle valve for controlling the combustion air of an internal combustion engine, into an emergency air position of the throttle valve.
2. Description of the Prior Art
When used in a throttle valve, a restoring device of this kind, in the event of a failure of the throttle valve drive unitxe2x80x94e.g. an electric motorxe2x80x94is used for restoring the throttle valve into a defined normal position, the so-called emergency air position or limp-home position, in which a minimal throttle valve opening is assured for the supply of combustion air to the internal combustion engine so that the engine continues to run smoothly at an idle or at a minimal load. Due to tolerances in the catches and due to the bending imprecision of the bent spring legs of the clamping spring, in the normal position in which the fixed catch and the driver catch are offset from each other radially and are disposed approximately congruently next to one another, there is a certain amount of play, which leads to a rotary play of the throttle valve and renders a precise control in this region impossible.
In a known restoring device for restoring a throttle valve contained in a throttle valve assembly in an internal combustion engine (DE 197 35 046 A1), oblique stop surfaces are provided on the fixed catch and driver catch in order to prevent rotary play between the catches in the normal position. The spring leg of the clamping spring, which leg is bent at the one spring end, is held against the oblique stop surfaces on the one side of the fixed catch and driver catch while the spring leg, which is bent at the other spring end of the clamping spring, is held against the flat stop surfaces extending parallel to the rotation axis on the other side of the fixed catch and driver catch. By means of the oblique stop surfaces, the spring leg is supported with half the respective spring force against the two oblique stop surfaces and as a result, moves the rotatable driver catch toward the stop constituted by the spring leg on the other side of the fixed catch and driver catch.
DE 100 13 917.5 has already proposed disposing a compensation spring, which has a definite spring force oriented counter to the prestressing force of the clamping spring, between a spring leg of the clamping spring and a stop surface on one of the catches in order to prevent a rotary play of the driver catch in the emergency air position. The compensation spring, which is manufactured as a stamped part, is affixed to one of the catches, with a spring leaf disposed in front of the one stop surface of the catch, which spring leaf rests with its free leaf end in a prestressed fashion against a spring stop, which limits the spring path of the spring leaf and is disposed spaced apart from the stop surface.
The restoring device according to the invention has the advantage that the play between the catches and the spring legs of the clamping spring in the normal position of the rotary member is prevented without additional parts, which would in turn necessitate manufacturing and installation expenditures, and therefore the characteristic curve of the clamping spring is not changed. The elastic spring element provided for this purpose on at least one of the two spring legs presses against the associated stop surface with a spring force that is less powerful than the prestressing force of the clamping spring in the normal position of the rotary member, so that as a result, in the normal position of the rotary member, the two spring legs rest against all four stop surfaces of the two catches and therefore prevent any play of the rotary member.
According to one advantageous embodiment of the invention, the spring element extends across a stop surface on the fixed catch and across a stop surface on the driver catch, and is constituted by one of the two spring legs of the clamping spring itself, in that the cross section of the spring wire of the clamping spring is reduced in the leg region of this spring leg and/or this spring leg is dimensioned to be of appropriate length. As a result, the at least one spring leg has an elasticity such that despite a width difference between the two catches, it rests against both stop surfaces and consequently does not permit any relative play between the two catches in the normal position of the rotary member.
In an alternative embodiment of the invention, a flexible tongue protruding from the leg section constitutes the spring element. Preferably, the flexible tongue is bent in one piece from the leg end of the spring leg. This has the advantage of a simpler manufacture of the spring element since the clamping spring must be bent at only one leg end before being hardened, which is relatively simple to achieve.
According to an advantageous embodiment of the invention, the catch whose stop surface is acted on by the flexible tongues is embodied with a width in the rotation direction of the driver catch that is always less than the width of the other catch, taking into to account permissible tolerances. As a result, the functionally optimal association of flexible tongue and stop surface is always assured in a reproducible manner.
According to another embodiment of the invention, in addition to the axial spring element, which extends across a respective stop surface of the fixed catch and the driver catch and which is comprised by one of the spring legs through cross sectional reduction or length measurement, an additional elastic spring element is disposed at the leg end of the spring leg, which additional spring element is embodied as a flexible tongue that is bent in one piece from the spring leg and rests in a prestressed fashion against a stop surface. In this embodiment of the restoring device, the two above-mentioned alternative possibilities for embodying an elastic spring element are embodied simultaneously in a leg section of at least one spring leg. This can be advantageous if a relatively large degree of play between the catches and the spring legs in the normal position of the rotary member is to be expected due to manufacturing conditions.